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POTENTIAL PURCHASE OF GAS-FIRED GENERATION FACILITY Additional Information (Details) (Entegra, Gila River Generating Station Unit 3, USD $)
In Millions, unless otherwise specified
Feb. 25, 2014
Dec. 23, 2013
MW
Unusual or Infrequent Item [Line Items]    
Potential Purchase of Gas-Fired Generation Facility   $ 219
Generating capacity of plant in MW   550
TUCSON ELECTRIC POWER COMPANY
   
Unusual or Infrequent Item [Line Items]    
Potential Purchase of Gas-Fired Generation Facility   164
Generating capacity of plant in MW   413
Percentage of ownership in Generating Unit   75.00%
Letters Of Credit Potential Amount 15  
UNS ELECTRIC, INC.
   
Unusual or Infrequent Item [Line Items]    
Potential Purchase of Gas-Fired Generation Facility   $ 55
Generating capacity of plant in MW   137
Percentage of ownership in Generating Unit   25.00%